Bacteria biofilms

Figure 4.21 schanaticaUy presents these mechanisms. The most important feature of the direct mechanism of bioleaching, as summarized by Nowaczyk and Domka, is that it involves biofilm formation by the bacteria. Biofilm, in this mechanism, acts as a medium for ion and electron exchange. This feature is no different from the way biofilm formation on metallic surfaces promotes biocorrosion. However, when it comes to the indirect mechanism, it does not require the attachment of the bacteria to the mineral. 

PVB is a natural polymer, produced in Burkholderia saccharin bacteria. Biofilms can be produced by casting processes. The films have been characterized by a variety of methods. The properties are highly influenced by the presence of a plasticizer, i.e., PEG. The thermal properties are comparable with domestic and industrial packing materials (19). 

Grobe, K. J. and Stewart, P. S., 2000. Characterization of Glutaraldehyde Efficacy Against Bacteria Biofilm. Corrosion/2000, Paper No. 124, (Orlando, FL NACE 2000). 

Lactic Acid Bacteria Biofilms From their Formation to their Health and Biotechnological Potential... 

Lactic Acid Bacteria Biofilms are Ubiquitous in a Wide Variety of Environments from Nature to Domesticated Settings... 

Agarwal, S., Sharma, K., Swanson, B.G., et al. (2006) Nonstarter lactic acid bacteria biofilms and caldum lactate crystals in Cheddar cheese. J Dairy Sci 89,1452-1466. 

Rhodospirillum salexigens is a marine bacterium, which has adhering properties to form bacteria biofilm. Zamamistatin (91) exhibited significant antibacterial activity against R. salexigens with an inhibition zone of 21 mm at 1.6 pg/disk, and may be a... 

Resistance to antimicrobial agents is of concern as it is well known that bacterial resistance to antibiotics can develop. Many bacteria already derive some nonspecific resistance to biocides through morphological features such as thek cell wall. Bacterial populations present as part of a biofilm have achieved additional resistance owkig to the more complex and thicker nature of the biofilm. A system contaminated with a biofilm population can requke several orders of magnitude more chlorine to achieve control than unassociated bacteria of the same species. A second type of resistance is attributed to chemical deactivation of the biocide. This deactivation resistance to the strong oxidising biocides probably will not occur (27). 

Biocorrosion of stainless steel is caused by exopolymer-producing bacteria. It can be shown that Fe is accumulated in the biofilm [2.62]. The effect of bacteria on the corrosion behavior of the Mo metal surface has also been investigated by XPS [2.63]. These last two investigations indicate a new field of research in which XPS can be employed successfully. XPS has also been used to study the corrosion of glasses [2.64], of polymer coatings on steel [2.65], of tooth-filling materials [2.66], and to investigate the role of surface hydroxyls of oxide films on metal [2.67] or other passive films. 

Fluvial biofilms (also known as phytobenthos or periphyton) are attached communities consisting of bacteria, algae and fungi embedded within a polysaccharide matrix [20]. In rivers, these communities are the first to interact with... 

Figure 6. Emission spectra from biofilms of estuarine bacteria exposed to ethanolic 4.5 x 10" M n-butyltrichlorotin and ethanolic 1.4 x 10" M flavonol (upper trace) and to flavonol only (lower trace).

Bacterial resistance to biocides (Table 13.2) is usually considered as being of two types (a) intrinsic (innate, natural), a natural property of an organism, or (b) acquired, either by chromosomal mutation or by the acquisition of plasmids or transposons. Intrinsic resistance to biocides is usually demonstrated by Gram-negative bacteria, mycobacteria and bacterial spores whereas acquired resistance can result by mutation or, more frequently, by the acquisition of genetic elements, e.g. plasmid- (or transposon-) mediated resistance to mercury compounds. Intrinsic resistance may also be exemplified by physiological (phenotypic) adaptation, a classical example of which is biofilm production. 

The non-random distribution of bacteria in biofilms has important applications for industry (biofouling, corrosion) and in medical practice (use of apphances within the human body). 

Microbial cells transported with the stream of fluid above the surface interact with conditioning films. Immediately after attachment, microorganisms initiate production of slimy adhesive substances, predominantly exopolysaccharides (EPS) that assist the formation of microcolonies and microbial films. EPS create bridges for microbial cells to the substratum and permit negatively charged bacteria to adhere to both negatively and positively charged surfaces. EPS may also control interfacial chemistry at the mineral/biofilm interface. 

SRB, a diverse group of anaerobic bacteria isolated from a variety of environments, use sulfate in the absence of oxygen as the terminal electron acceptor in respiration. During biofilm formation, if the aerobic respiration rate within a biofilm is greater than the oxygen diffusion rate, the metal/biofilm interface can become anaerobic and provide a niche for sulfide production by SRB. The critical thickness of the biofilm required to produce anaerobie conditions depends on the availability of oxygen and the rate of respiration. The corrosion rate of iron and copper alloys in the presence of hydrogen sulfide is accelerated by the formation of iron sulfide minerals that stimulate the cathodic reaction. 

A simplification of the polarization resistance technique is the linear polarization technique in which it is assumed that the relationship between E and i is linear in a narrow range around E . Usually only two points ( , 0 are measured and B is assumed to have a constant value of about 20 mV. This approach is used in field tests and forms the basis of commercial corrosion rate monitors. Rp can also be determined as the dc limit of the electrochemical impedance. Mansfeld et al. used the linear polarization technique to determine Rp for mild steel sensors embedded in concrete exposed to a sewer environment for about 9 months. One sensor was periodically flushed with sewage in an attempt to remove the sulfuric acid produced by sulfur-oxidizing bacteria within a biofilm another sensor was used as a control. A data logging system collected Rp at 10-min intervals simultaneously for the two corrosion sensors and two pH electrodes placed at the concrete surface. Figure 2 shows the cumulative corrosion loss (Z INT) obtained by integration of the MRp time curves as ... 

H2S production caused by the growth of sulfate-reducing bacteria in a biofilm in the reservoir rock close to the injection well (biofilm model)... 

E. D. Burger, A. B. Crews, and H. W. Ikerd, n. Inhibition of sulfate-reducing bacteria by anthraquinone in a laboratory biofilm column under dynamic conditions. NACE Int Corrosion Conf (Corrosion 2001) (Houston, TX, 3/11-3/16), 2001. 

M. J. Franklin, D. E. Nivens, A. A. Vass, M. W. Mittelman, R. F. Jack, M. J. E. Dowling, and D. C. White. Effect of chlorine and chlorine/bromine biocide treatments on the number and activity of biofilm bacteria and on carbon steel corrosion. Corrosion, 47(2) 128-134, February 1991. 

P. J. Robinson, J. T. Walker, C. W. Keevil, and J. Cole, Reporter genes and fluorescent-probes for studying the colonisation of biofilms in a drinking-water supply line by enteric bacteria. FEMS Microbiol. 729 183 (1995). 

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